package org.apache.ocean.util;

/**
 * <code>BitDocSet</code> represents an unordered set of Lucene Document Ids
 * using a BitSet.  A set bit represents inclusion in the set for that document.
 *
 * @author yonik
 * @version $Id: BitDocSet.java 498246 2007-01-21 05:46:31Z yonik $
 * @since solr 0.9
 */
public class BitDocSet extends DocSetBase {
  final OpenBitSet bits;
  int size;    // number of docs in the set (cached for perf)
  
  public BitDocSet(int size) {
    bits = new OpenBitSet(size);
  }
  
  public BitDocSet() {
    bits = new OpenBitSet();
  }
  
  /** Construct a BitDocSet.
   * The capacity of the OpenBitSet should be at least maxDoc() */
  public BitDocSet(OpenBitSet bits) {
    this.bits = bits;
    size = -1;
  }
  
  /** Construct a BitDocSet, and provides the number of set bits.
   * The capacity of the OpenBitSet should be at least maxDoc()
   */
  public BitDocSet(OpenBitSet bits, int size) {
    this.bits = bits;
    this.size = size;
  }
  
  public DocIterator iterator() {
    return new DocIterator() {
      private final BitSetIterator iterator = new BitSetIterator(bits);
      private int pos = iterator.next();
      public boolean hasNext() {
        return pos >= 0;
      }
      
      public Integer next() {
        return nextDoc();
      }
      
      public void remove() {
        bits.clear(pos);
      }
      
      public int nextDoc() {
        int old = pos;
        pos = iterator.next();
        return old;
      }
      
      public float score() {
        return 0.0f;
      }
    };
  }
  
  /**
   *
   * @return the <b>internal</b> OpenBitSet that should <b>not</b> be modified.
   */
  public OpenBitSet getBits() {
    return bits;
  }
  
  public void add(int doc) {
    bits.set(doc);
    size = -1;  // invalidate size
  }
  
  public void addUnique(int doc) {
    bits.set(doc);
    size = -1;  // invalidate size
  }
  
  public int size() {
    if (size != -1) return size;
    return size = (int)bits.cardinality();
  }
  
  /**
   * The number of set bits - size - is cached.  If the bitset is changed externally,
   * this method should be used to invalidate the previously cached size.
   */
  public void invalidateSize() {
    size = -1;
  }
  
  public boolean exists(int doc) {
    return bits.get(doc);
  }
  
  public int intersectionSize(DocSet other) {
    if (other instanceof BitDocSet) {
      return (int)OpenBitSet.intersectionCount(this.bits, ((BitDocSet)other).bits);
    } else {
      // they had better not call us back!
      return other.intersectionSize(this);
    }
  }
  
  public int unionSize(DocSet other) {
    if (other instanceof BitDocSet) {
      // if we don't know our current size, this is faster than
      // size + other.size - intersection_size
      return (int)OpenBitSet.unionCount(this.bits, ((BitDocSet)other).bits);
    } else {
      // they had better not call us back!
      return other.unionSize(this);
    }
  }
  
  @Override
  public int andNotSize(DocSet other) {
    if (other instanceof BitDocSet) {
      // if we don't know our current size, this is faster than
      // size - intersection_size
      return (int)OpenBitSet.andNotCount(this.bits, ((BitDocSet)other).bits);
    } else {
      return super.andNotSize(other);
    }
  }
  
  public DocSet andNot(DocSet other) {
    OpenBitSet newbits = (OpenBitSet)(bits.clone());
    if (other instanceof OpenBitSet) {
      newbits.andNot(((BitDocSet)other).bits);
    } else {
      DocIterator iter = other.iterator();
      while (iter.hasNext()) newbits.clear(iter.nextDoc());
    }
    return new BitDocSet(newbits);
  }
  
  public DocSet union(DocSet other) {
    OpenBitSet newbits = (OpenBitSet)(bits.clone());
    if (other instanceof BitDocSet) {
      newbits.union(((BitDocSet)other).bits);
    } else {
      DocIterator iter = other.iterator();
      while (iter.hasNext()) newbits.set(iter.nextDoc());
    }
    return new BitDocSet(newbits);
  }
  
  public long memSize() {
    return (bits.getBits().length << 3) + 16;
  }
}
